73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Electrical => Topic started by: 502Silverado on January 09, 2019, 08:56:35 PM
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I apologize for the long post, just trying to be thorough. I did a search for my specific issue and couldn't find an answer.
I have an 87 R10 350 TBI that I have recently replaced the battery, the inner passenger fender, bushings under the core support and cab, radiator, headlights, shocks front and rear, rear brakes and had the original core support sandblasted and then I rattle can painted it myself. I finally drove it to work today after working on it for about 5 months and noticed that the voltmeter is nearly pegged at the 18 mark (original gauges, stock engine) whenever the throttle is applied. When at idle it reads just past the 13 on the gauge. When I accelerate or traveling at constant speed is when the gauge nearly pegs. I have not noticed any fluctuations in the headlights/tail lights, interior or dash lights. The left turn signal does seem to blink a little slow and the oil pressure gauge slowly drops to zero but I believe that is a sending unit issue.
I'm thinking it could be a grounding issue? I have not used a ohm meter at all because I know more about the gross national product of Zimbabwe than electricity.
Any help or advice is greatly appreciated.
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Check the actual voltage with a voltage meter to verify the accuracy of the gauge.
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Just buy a cheap VOM at Walmart or the auto parts store. It should not be more than about $10-$12, or even cheaper if you have a Harbor Freight nearby and can buy one like this https://www.harborfreight.com/7-function-digital-multimeter-63604.html .
Check the voltage at idle with the negative meter lead grounded to the engine or alternator bracket, and the positive meter lead on the BAT post of the alternator (the threaded terminal on the back of the alternator), or on the battery positive. It should read about 12.5-13.0 volts while idling, and then go up to about 13.8-14.0 volts when you raise up the RPM.
If you get a reading of anything more than about 14.5 volts, the voltage regulator is not working right. You can buy a new regulator, but it might be simpler to just get a rebuilt alternator.
Bruce
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Thanks for the replies. I cleaned all the ground connections today and plan on picking up a multimeter tomorrow. Thanks for letting me know where to connect everything, electrical systems are definitely not my thing.
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Ok, I connected a multimeter to the battery while it was off and got around 12.5 or so. Once it was started it went to about 14. When I gave it a little gas (I don't have tach) it jumped to above 15. I also noticed that whenever I turned on the heater it dropped off quite a bit. I'm assuming that my regulator for the alternator is bad due to how high the multimeter jumped when I gave it a little gas? Thanks for the help.
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Ground the negative lead of the voltmeter to the alternator case, set the parking brake, start the engine and probe the negative terminal of the battery with the positive voltmeter lead, both at idle and at very fast idle (~2,000 RPM). If the alternator is properly grounded, the measurement should be zero or very nearly zero. Next, probe the #2 (or "F") regulator lead that plugs into the rearward side of the alternator case (red wire in the two-wire connector imaged below). Post the results.
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Thanks, bd. It will be a few days before I get a chance to do that. I actually borrowed the multimeter from an electrician that was building the house next door to me. Gonna try and pick up one of my own.
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Purchase a digital meter as opposed to analog. For occasional use, figure on spending between $20 and $30.
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If this is your first multimeter, consider both price and whether you plan to use it for something other than your car.
I think most digitals are high impedence, (but I'm not sure) which works well if you also want to use it for more sensitive electronics (stereos, HVAC controls, etc.). However, the downside of a high impedence meter is that on basic tasks (checking for voltage before replacing a light switch, etc.) it may pick up stray voltage in house wiring when wires are bundled together. I've had this issue with house wiring, where I measured voltage at a light switch and it never dropped completely to zero because it was picking up ghost voltage from wiring next to it.
When you use a digital meter, also make sure its set to measure DC voltage, not AC. My Klein meter will default to AC when you turn it on, which gets confusing when you are working with DC. I spent several minutes trying to troubleshoot a DC circuit in a radio before realizing the meter was set to AC volts.
Bruce
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Ok, thanks for being patient with me. I started looking at multimeters and quickly got over whelmed with specs and brands and prices and decided to borrow one from my father.
With the truck off the battery is reading 12.51
While cranking it drops to 10.40 or so
Once started and at idle it was reading 15.9
With lights, radio and heater on it would fluctuate between 15.00 and 15.20
All of the above were read at the battery.
I took a reading with the negative lead of the meter on the alternator case and positive lead on the negative battery terminal and got .01
I next took readings with the negative lead of the meter on the grounds (frame, firewall, and both on the core support) and the positive lead on the negative battery cable. None of those were above .01 and some were all zeros. When reading the grounds and at the alternator case it was slightly above idle speed.
I attempted to read from the #2 on the alternator with the negative lead from the meter and the positive on the negative battery terminal but I don't believe I was making contact because the meter never registered anything.
While doing all this and letting the truck go back to idle the meter read 15.12 at the battery with no lights, radio or heater on. I also took a reading with the negative lead of the meter on the screw terminal on the back of the alternator and the positive meter lead on the negative battery terminal. It was also 15.12.
I'm thinking the regulator may be bad from everything I've read so far. I have not checked the actual gauge in the dash.
Hope this helps and thanks to you both!
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I think regulator is bad too. Usual voltage while running, I have known about, is 13.5-14.5. Does your alternator have internal regulator? I am not up to date with 87 but it may, then new alternator is needed.
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Yes, its an internal regulator.
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Before you condemn the alternator you need to verify the running voltage on the #2 regulator terminal as previously described. The #2 regulator terminal is the voltage sensing input to the regulator. If the running voltage on that terminal is "zero" as you described the alternator will charge uncontrollably. The voltage on the #2 terminal should match the output voltage at the B+ post on the back of the alternator. If the #2 terminal measures 15.9+ volts with the engine running, replace the alternator.
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Sorry, I知 an idiot. I was trying to get a reading from where the red wire where they plugged into the alternator instead of just following that wire to the screw post on the back of the alternator where access is easier. I値l try there.
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No, you were on the right track. With the engine running, measure the voltage on the #2 regulator terminal and compare that to the voltage on the B+ output post at the back of the alternator. The two measurements should match. Then unplug the two-wire connector and make sure the wire terminals are clean, intact and fit snug on the regulator pins. If the voltage measurements are identical and there are good wire connections to the regulator, replace the alternator. On the other hand, if the voltage measurements are not the same, repair the wire or its connections between the B+ post and the #2 regulator terminal. Capiche?
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I think I知 with you. Forgive my ignorance, but I probe the #2 on the alternator with the NEG lead on the multimeter and the POS lead of the multimeter on the NEG battery terminal? Also, I知 assuming to test the #2 I can just insert the lead into the connector so that it is next to the wire?
This morning I did connect the NEG meter lead to the red wire terminal end (where the red wire from the two wire connector attaches to the B+ on the alternator. Those numbers were the same as when testing at the battery.
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I had the same problem with my 1967 Chevelle SS. I ran a ground wire to voltage regulator and solved the problem. Good luck with your high voltage problem.
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The 67 Chevelle used an external regulator. DO NOT run a ground wire to the regulator of an internally regulated alternator!
An abbreviated orientation to the 1987 R10 charging system:
The alternator is a self-regulating, "dynamic" power source that functions only while the engine is running. The purpose of the alternator is to charge and compliment the battery, which is a "static" power source that remains somewhat constant through chemical processes (assuming no external influences are present). Together, the alternator and battery form an interdependent system. The alternator maintains battery full-state-of-charge by regulating alternator output at a predetermined fixed voltage that lies within the range of 14.2 - 14.7 volts. The regulator calibration determines the exact voltage within that limited range. A fully charged "12-volt" lead-acid automotive battery actually produces 12.6 volts. Therefore, the difference in voltage (dV) between the battery when fully charged and the alternator output while the engine is running is approximately 2 volts. That's not very much. Due to a fixed direct relationship between voltage and current, dV determines the current demand imposed on the alternator. In other words, as the battery discharges its voltage drops and dV increases. Consequently, alternator current output to recharge the battery increases in direct proportion.
Why is this relevant? The key is that the regulator controls the voltage output of the alternator by monitoring the voltage at the B+ output post on the back of the alternator via the short external jumper previously pictured. If there is a poor connection or open in the jumper wire running between the B+ post and the regulator #2 terminal, the regulator cannot "see" the alternator output voltage and the alternator will charge uncontrollably (otherwise known as "full-fielding"). Since the alternator is a power source, the regulator is concerned only with the output from the alternator. Therefore, the relevant voltage measurements are between the alternator case (as ground) and the B+ post, and between the alternator case (as ground) and the #2 regulator terminal. If the voltage measurements are identical, either the regulator or an internal connection has failed and the alternator should be replaced.
...I probe the #2 on the alternator with the NEG lead on the multimeter and the POS lead of the multimeter on the NEG battery terminal?...
No. The negative probe of the meter connects to the alternator case (ground) and the positive lead is used to probe for voltage at the #2 terminal and the B+ output post. By using the alternator case as the ground connection point, you eliminate any variables that may be introduced by faulty ground connections that could exist between the alternator and the battery.
...I知 assuming to test the #2, I can just insert the lead into the connector so that it is next to the wire....
Correct.
Did this help clarify the circumstances?
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Gotcha. Thanks for your patience. I値l look at it again this evening.
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Ok, just got done again. Probing the #2 red wire with the POS lead of the meter and the NEG lead of the meter on the alternator housing resulted in a 15.40 or so reading. Same results when on the B+ post on the alternator.
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There ya go.
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Thanks for all of your help. Now I gotta figure out what size alternator it is and the size I need.
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Disregard. K22 RPO code is a 94 amp alternator.
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Not to be a killjoy, but referring back to your original post, once you resolve the charging system overvoltage don't be surprised if you still have a voltmeter issue.
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All right. You have my attention....
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Only that once the charging system is under control you may discover that the voltmeter is still registering a slightly high voltage. It may be within acceptable limits and tolerable, considering that the OEM gauges are not precision instruments. So not to worry about it before that bridge is in sight. Just be aware to avert disappointment.
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Gotcha. Thanks again for your patience and help. I can honestly say I learned something.